Process for removing acid components from hydrocarbon distillates



V Patented Aug. 20, 1940 PATENT OFFICE rnoonss' FOR REMOVING ACID ooMro- NENTS FROM LATES HYDROCARBON DISTIL- David Louis Yabrofl, Berkeley, Calif., assignor to Shell Development Company, San Francisco, Calif., a corporation of Delaware No Drawing.

6 Claims.

This invention is a continuation-in-part of my co-pending application Serial No. 102,893, filed September 28, 1936, which has issued as I ,S. 1

Patent 2,152,166, March 28, 1939, and deals with the removal of weakly acid. reacting organic substances from solutions in certain water-insoluble organic liquids by extraction with aqueous solutions ofcaustic alkali containing a solubility promoter for these substances, and more particularly deals with the removal of mercaptans from hydrocarbon distillates.

It, is frequently necessary to eliminate small quantities of organic relatively weak acid reacting components such as mercaptans, phenols, thiophenols, 'alkyl phenols, fatty acids, etc., from their solutions in neutral or weakly basic reacting organic liquids which are substantially immiscible containing hydrocarbons such as amyl or higher amines, aniline, water-insoluble pyridine derivatives, petroleum bases, etc.

In order that the water-insoluble organic liquids may be treated by my process, they must be substantially inert and resistant to chemical reaction with strong aqueous solutions of caustic alkali when contacted therewith for short periods of time,e. g., about. 10 minutes or less at normal room temperatures.

My invention comprises extracting organic acids which are diflicult to extract, such as the weak acids having dissociation constants lower than those of fatty acids, e. g., mercaptans, phenols, etc., contained in water-insoluble organic liquids which are substantially inert toward strong aqueous caustic alkali solutions at normal room temperatures, with an aqueous solution of caustic alkali in which is dissolved a substantial amount of a solubility promoter for weak organic acids, under conditions'to absorb at least a major portion of the weak organic acids in the aqueous solution, and toiorm two layers and separating the layers.

In the application Serial No. 102,893, filed September 28, 1936, I have disclosed that certain polar substances which are at least partly miscible with aqueous solutions of strong caustic alkali, promote the solvent power for weak organic acids of aqueous caustic alkali solutions in which Application February 7, 1939, Serial No. 255,103'

theyare dissolved. I have shown that among other compounds, certain glycols, including triethylene glycol are highly effective in the matter of promoting the solubility of weak organic acids such asmercaptans, phenols, etc., in aqueous caustic alkali solutions.

Aqueous solutions of various caustic alkalis may be used. The alkali metal hydroxides are most useful and effective, although ammonia,

alkaline earth hydroxides, quaternary ammonium bases, alkali metal carbonates, etc., may also be suitable,

The concentration of the aqueous caustic alkali may vary within wide limits. In general, I prefer to, use caustic alkali solutions which are above about 2 normal and preferably between 4 to 10 normal, calculated on the total solution, although higher and lower concentrations may be used.

Concentration of the triethylene glycol in the aqueous solution should preferably be between about 25 and, 75%. Moreover, the amount of water in the solution should be not less than 15% and not more than 70%, preferably not more than The presence of water in the above amount is highly desirable because otherwise the regeneration by steam stripping of spent alkaline solution containing solubility promoter and absorbed weak organic acids is extremely dimcult. Thus steam consumption is greatly reduced by the presence of the preferred amounts of water, while on the other hand, the extraction eiiioiency for the weak acids need not be reduced materially. The presence of amounts of water greater than 15% does not cause a substantial hydrolysis of dissolved alkali salts of the weak organic acids ashas been supposed by earlier investigators, the hydrolysis being largely a function of the alkalinity of the aqueous solution.

While increasing the amount of water may have the additional advantage of reducing losses of the triethylene glycol due to its being dissolved in the organic liquid, this is a minor consideration when treating hydrocarbon liquids, because .triethylene glycol is substantially insoluble in hydrocarbon liquids even in the presence of amounts of water much smaller than 15%. Thus, for example, when contacting isooctane with 20 volume percent of aqueous solutions of triethylene glycol containing 10 and 15% water, respectively, and analyzing the resulting isooctane for the glycol, it was found that the amount of glycol in the isooctane was 04% and .03%.

Triethylene glycol is a far more powerful solubility promoter for weak organic acids than ethylene glycol. In fact, under my conditions.

K concentration of mercaptans in aqueous phase concentration of merceptans in oil phase Solubility promoter K value None. 1. 6 ethylene glycol l. 5 o triethylene glycol l2. 5

The temperature of the extraction is preferably kept between 0 and 6011, the extraction efflciency decreasing with increases in the temperature; and at temperatures below about 0 C. difliculties are frequently encountered due to precipitation of a portion of the solubility promoter and/or excessive viscosity of the aqueous caustic alkali containing the solubility promoter.

The extraction of the organic acids from their solutions in the organic liquids described before may be carried out by simply mixing the solution with a predetermined amount of the aqueous caustic alkali solution in which is dissolved a substantial amount of the triethylene glycol, and then separating the liquids. The resulting aqueous solution contains most of the triethylene glycol and the major portion of. the organic acids, while the organic liquid stripped from the acids contains a trace of the glycol. By washing the stripped organic liquid with water, the triethylene glycol is re-extracted by the latter. The aqueous solution so obtained may then be added to the caustic alkali solution'containing the bulk of the glycol, and excess water may be separated from the resulting solution by distillation.

More thorough extraction may be had, however, in a multi-stage countercurrent extraction system or in a packed tower.

The amount of aqueous caustic alkali solution required in the extraction is normally above about 5% by volume and for economical reasons seldom exceeds about 100% by volume. Normally from about 10 to by volume is used depending upon the required thoroughness of removing the I weak organic acids.

Spent aqueous caustic alkali solution containing the triethylene glycol and weak organic acids may be regenerated by distillation, steaming and/or oxidation, according to well-known principles.

of triethylene glycol, said solution containing The following example further serves to illustrate my process:

A West Texas straight run full range gasolinecontaining .0778% mercaptan sulfur was extracted at 20 C. with 20volume' percent of a 2.5 5 N aqueous caustic soda solution. 14.6% of the mercaptan sulfur was removed. When treating the same gasoline under identical conditions with a 2.5 N aqueous caustic soda solution containing 50% triethylene glycol, 30.5% of the mercaptan 1 sulfur was removed.

I claim as my invention:

1. In the process of separating organic acid reacting substances contained in a water-insoluble neutral or basic organic liquid, the steps 15 comprising treating said liquid with an aqueous solution, of a strong base containing a substantial amount of dissolved triethylene glycol, said solution containing from 15 to water, under conditions to absorb at least a portion of said acid reacting substances in said aqueous solution and to form two liquid layers one comprising the aqueous solution containing absorbed acid reacting substances, and the other consisting essentially of the treated organic liquid and separating the layers.

2. The process of claim 1 in which the aqueous base solution contains between 25am! of the triethylene glycol. a

3. The process of claim 1 in which the aqueous base is from 2 to 10 normal.

4. The process of claim 1 in which the organic liquid is extracted with 5 to volume percent of aqueous base solution containing'th'e triethylene glycol.

5. The process of claim 1 in which the base is an alkali metal hydroxide.

6. In the process of separating mercaptans from hydrocarbon distillates containing same by extraction with an aqueous solution of a strong base, the improvement comprising extracting said distillate with at least 5 volume per cent of a 2 to 10 normal aqueous alkali metal hydroxide solution in which is dissolved between 25 and 75% from 15 to 70% water, under conditions to absorb at least a major portion of the me'rcaptans in the aqueous solution and to form two liquid layers, one comprising the aqueous alkali metal hydroxide solution containing substantially all of the triethylene glycol and the major portion of the mercaptans, and the other consisting essentially of treated hydrocarbon distillate, and separating the layers.

DAVID LOUIS YABROFF. 

